This invention relates to an optical scanning system and particularly to a compact optical scanning system for a reproducing machine capable of producing copies from originals of more than one magnification.
In a typical reproducing machine the optical scanning system reflects light rays or images from successive portions of an original document which is held on a transparent viewing platen. The light rays are provided by an illumination source which together with a reflector or mirror is supported for movement relative to the document supported on the viewing platen. As the mirror moves past the document, the light rays reflected from the document strike the mirror and are reflected onto another mirror from which they are directed through a lens and finally onto a photosensitive material which typically is a rotatable drum, the drum being adapted for movement in the same direction and at the same speed as the illumination source and first mirror discussed above.
In the foregoing manner, images of successive portions of the original document are flowed onto successive portions of the photosensitive drum to thereby produce a latent image of the document in accordance with well known techniques. In providing a copy of the document by the foregoing type of optical projection system it is necessary to maintain constant the distances over which the light rays travel from the document to the lens and from the lens to the photosensitive drum or at least a constant ratio therebetween should be maintained. This can be accomplished by the provision of a stationary lens and first and second mirror assemblies which direct the rays from the document and which are movable with respect to one another, the second mirror assembly being moved at one half the speed of the first mirror assembly whereby the document to lens distance is maintained constant. Such a copying apparatus is capable of producing copies of the original at one magnification which is usually a one-to-one ratio.
With the continued development and increasing use of reproduction machines it has been increasingly desired and popular to provide reproduction capability in the machine at more than one magnification. In the past copies at more than one magnification have been provided by using a plurality of lenses having different magnifying powers and substituting one lens for another according to the degree of magnification desired.
Another apparatus for producing copies of originals at different magnifications simultaneously moves the lens and reflecting mirrors, the lens generally being moved a much smaller distance than the mirror. By so doing the length of the object conjugate, the length of the optical path from the object plane to the lens, and the image conjugate, the length of the optical path from the lens to the image plane, are changed. For a one-to-one magnification, the object conjugate and image conjugate are equal. For a reduction magnification the object conjugate is longer than the image conjugate. In addition, in such a system in obtaining a less than one-to-one magnification the original is generally scanned at a faster rate. In still other similar systems with variable magnification an add lens may be provided to compensate for lens movement.